1. Field of the Invention
This invention relates to a disk casing, and more particularly to a disk casing for accommodating a recording medium such as a CD or a DVD.
2. Description of the Related Art
As shown in FIG. 2, a three-piece disk casing 1′ which is 10 mm in thickness and has been commonly used comprises a plastic disk tray 3 having at a central portion of an upper surface thereof a disk damper 2 which is engaged with a central opening of a disk (not shown) to removably support the disk, a transparent plastic lower lid 4 which has a flat principal surface (a flat outer surface having a wide area) 4a to removably accommodate and fix the disk tray 3, and a transparent plastic upper lid 5 which has a flat principal surface 5a and is pivoted on the lower lid 4 to be opened and closed about an axis L with respect to the lower lid 4.
The upper lid 5 has a pair of side walls 5b and pair of hinge arms 5c which are extensions of the respective side walls 5b at one end thereof, and short shafts 6a extend inward from the respective hinge arms 5c. By engagement of the short shafts 6a in pivot holes 7 formed in side walls 4b of the lower lid 4 along the axis L, the upper lid 5 is pivoted on the lower lid 4 to be opened and closed about an axis L.
As shown in FIG. 3, the disk tray 3 comprises an elongated end portion 10 which extends along an end wall 11 of the lower lid 4 on the side of the axis L and has an upper surface 10a facing upward substantially flush with the principal surface 5a of the upper lid 5 when the casing 1′ is closed and adjacently to the principal surface 5a. The end portion 10 is abutted against an upper end face 11a of the end wall 11 of the lower lid 4 on the side of the axis L and is supported thereby.
An upper index card 12 is held on the back side of the upper lid 5 by a plurality of retainer pieces (not shown) and a lower index card 14 is interposed-between a bottom surface 3a of the disk tray 3 and an inner bottom surface 4c. An end portion of the lower index card 14 on the side of the end portion 10 of the disk tray 3 is bent upward by about 90° along an inner surface 11b of the end wall 11 of the lower lid 4 on the side of the axis L to form a backbone 14a visual from outside through the transparent end wall 11.
However, the lower index card 14 in a 10 mm thick disk casing 1′ having such structure is limited in the height h′ of the backbone 14a by the height of the end wall 11 of the lower lid 4 from the inner bottom surface 4c thereof and is 6 mm or so at most, and accordingly, what is recorded on the backbone 14a is hard to read. Especially, when a number of disk casings are stacked or are accommodated in a rack in an arranged state, the upper index card 12 held in the upper lid 5 and the part of the lower index card 14 opposed to the principal surface 4a of the lower lid 4 both become invisible and what is recorded on the backbone 14a is harder to read.
In order to overcome this problem, there have been proposed various disk casings. For example, in Japanese Unexamined Patent Publication No. 2004-091042, there has been proposed an optical disk casing in which the end wall of the lower lid 4 outside the back bone on the lower index card 14 is a convex lens. However, this structure is disadvantageous in that the outer contour of the disk casing must be changed, and at the same time, the disk casings employing the structure are harder to store as compared with other standard type disk casings.
Further, the part of the disk casing in the form of the convex lens involves a complicated structure of the molding dye called “undercut”. Further, the part of the disk casing in the form of the convex lens deteriorates the productivity when molding the disk casing.